doc/go1.22: document openbsd/ppc64 port

Updates #56001.
For #61422.

Change-Id: Ie4afbc42191b155d28945bd8f104ad7a63d30db9
Reviewed-on: https://go-review.googlesource.com/c/go/+/547999
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>

Author: cherrymui

doc/go1.22.html

@@ -805,9 +805,10 @@ <h3 id="loong64">Loong64</h3>
   The <code>linux/loong64</code> port now supports the memory sanitizer, new-style linker relocations, and the <code>plugin</code> build mode.
 </p>
 
-
+<h3 id="openbsd">OpenBSD</h3>
 <p><!-- CL 517935 -->
-  TODO: <a href="https://go.dev/cl/517935">https://go.dev/cl/517935</a>: cmd/dist,internal/platform: enable openbsd/ppc64 port
+  Go 1.22 adds an experimental port to OpenBSD on big-endian 64-bit PowerPC
+  (<code>openbsd/ppc64</code>).
 </p>